A detector may be used, for example, to detect X-radiation in an X-ray unit, for example in a computed tomography unit. The detector generally includes a number of detector modules that are arranged in a row one after another or in two dimensions to form a larger detector surface. Each detector module has a scintillator array and a photodiode array that are aligned relative to one another and connected to one another by an adhesive that also serves as an optical coupling layer. The scintillator array has a multiplicity of scintillator elements that are separated from one another by inactive areas, so called septa. The photodiode array also has a multiplicity of photodiodes that are separated from one another by inactive zones.
If, during operation of the X-ray unit, X-radiation that has passed through an examination object, for example a patient, and is therefore attenuated, strikes an element of the scintillator array, it is converted into visible light. The visible light is guided through the optical coupling layer in the form of the adhesive to the photodiode, assigned to the element of the scintillator array, of the photodiode array, which converts the visible light into electric signals. The electric signals originating from the photodiodes of the photodiode array are subsequently processed further. Images of the examination object are reconstructed from the measurement signals that have been further processed, this being done with the aid of a computer.
When converting X-radiation into visible light in a scintillator element, the problem arises that the visible light produced is intrinsically scattered diffusely. It follows that there is an undirected exit of the light into the optical coupling layer from the scintillator element on the side thereof assigned to a photodiode. Consequently, a portion of the light produced in the scintillator element is not passed directly on to the photodiode assigned to the scintillator element, but undesirably reaches an adjacent photodiode, which is assigned to another scintillator element, bilateral crosstalk along the optical coupling layer. This fraction of the light produced by the scintillator element is therefore defective for signal evaluation. Moreover, a portion of the light produced by the scintillator element passes into the inactive zones present between the photodiodes and so this fraction of the light produced in the scintillator element is lost for signal evaluation.
In order to counteract these effects at least in part, to date a scintillator array and a photodiode array have been connected with the aid of an optically adjustable position system in order to achieve the best possible layer thickness of the optical coupling layer in the form of the adhesive. The optimal layer thickness constitutes a compromise in this case. In order to avoid the crosstalk, the layer thickness of the coupling layer should be as small as possible.
On the other hand, however, a minimum layer thickness of the adhesive is necessary with regard to the technical feasibility, interspace between the scintillator array and the photodiode array requiring to be completely filled up despite planarity tolerances of the components and the viscosity of the adhesive, in order to achieve coupling of the scintillator array to the photodiode array. There proves to be a problem here in achieving a uniform layer thickness of the adhesive over the entire detector module comprising the scintillator array and the photodiode array.